Hi Ralf,
I guess you're processing the message by debugging in SPROXY?
When an FEH-case shall be created the message UUID must correspond to an existing message in SXI_MONITOR.
An additional hint:
The information whether an FEH case is created isn't stored in some AMI-table but it checked whether for the message there exists an entry in /SAPPO/ORDER_HDR.
Best regards
Harald